The present invention relates to a multi-stage internal combustion engine for vehicles comprising two or more power units, which are combined in response to a driving condition of the vehicle for effectively generating power.
FIG. 1 shows a fuel consumption characteristic of a conventional engine at various specific fuel consumptions (g/ps.hr), in which the abscissa is engine speed (r.p.m.), and the ordinate is torque. Curve A shows the running load (resistance) of a vehicle on a flat road. The curve A is determined by the air resistance of the body of the vehicle and the gear ratio of the transmission of the engine and the specific fuel consumption is decided by the performance of the engine. It is desirable to design the engine that the curve A passes through low fuel consumption zones.
FIG. 2 shows a fuel consumption characteristic of an engine according to the present invention comprising two power units. The first zone C is characteristic of the first power unit and the second zone E is characteristic of the engine in which the first power unit and the second power unit are combined. The fuel consumption characteristic of the second zone is the same as that of the conventional engine shown in FIG. 1 and the runnning load curve B is the same as the curve A. If the curve B passes through a minimum fuel consumption zone D at a small torque operation as shown in FIG. 2, fuel consumption is improved.